Common user actuated switches utilize rocker or push button style actuators to close contacts on a printed circuit board (PCB) or contact unit. The two most common methods to make this contact closure are to use microswitches or rubber domes, but rubber domes are susceptible to contamination.
Microswitches used for customer actuated switch (CAS) applications are typically sealed from contamination and rated for automotive use to assume proper function in extreme conditions and high cycle life. Depending on switch design, the microswitch might also have a preload stroke to absorb the manufacturing tolerances of the components and eliminate any buzz, squeak, or rattle conditions. The actuation force of the microswitch from excessive forces that can occur after contact closure is made. Unfortunately, these microswitches are generally cost prohibitive.
One alternative is to use an elastomer pad with integral buttons, also referred to as rubber dome pad or mat. With this design, a carbon or plated (Au or Ag) disk-shaped contact is insert molded inside each contact dome on the mat. The mat is placed over the surface of a PCB and the dome contacts align with the contact closures on the PCB surface. The switch actuator, either rocker or push button, collapses the rubber dome and the contact disk makes a connection across the contact closure on the PCB. Tactile force and stroke can be controlled by the design of the rubber dome. Although this design is less expensive than sealed microswitches, contamination is an inherent problem. The elastomer pad is not sealed to the PCB, and there is a tendency for the contamination to be drawn in the contact area as the dome returns to the open position.
Accordingly, there is a need for a switch assembly that is sealed from contamination, can meet specified tactile requirements for a CAS, i.e. force and tactile feel, and is cost effective and reliable.